Chert (Jasper/Flint variety)

Physical Properties

Hardness: 7 on Mohs scale. Color: Brown, tan, and reddish-orange due to iron oxides. Luster: Dull to waxy. Crystal structure: Cryptocrystalline (microscopic quartz crystals). Cleavage: None, exhibits conchoidal (shell-like) fracture.

Formation & Geological History

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or through chemical precipitation in sedimentary environments. Often found as nodules in limestone or chalk beds.

Uses & Applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in road construction as aggregate and occasionally as semi-precious gemstones for jewelry (Jasper/Agate).

Geological Facts

Chert was one of the most important minerals for early humans because of its ability to be knapped into sharp tools. It is also used as a fire-starter when struck against steel to create sparks.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass and steel) and its smooth, curved conchoidal fractures. Commonly found in riverbeds, glacial till, and limestone outcrops globally.

Identified on: 4/28/2026

Mode: Standard